Process for the recovery of protassium salts from solutions



' Oct 7, 1941,` w. FLEISCHER ETAL 2,258,381

PROCESS FOR THE RECOVERY OF POTASSIUM SALTS FROM SOLUTIONS Filed July21, i939 Patented Oct. 7, 1941 UNITED STATES PROCESS FOR THE RECOVERY OFPOTAS- SIUM SALTS FROM SOLUTIONS Wilhelm Fleischer and Jacob Kielland,Porsgruml,

Norway, assignorsv to Kvaelstofaktieselskab,

Norsk Hydro-Elektrisk Oslo, Norway Application July 21, 1939, Serial No.285,794 In Norway July 29, 1938v `8 Claims.

The present invention relates to a novel method for the recovery ofpotassium salts from solutions, particularly solutions with a relativesmall content of potassium, such for example as sea which can beseparated fromthe solutionby filtration, decantation, or otherwise.

Instead of' the calcium dipicrylaminate, vuse mayalso be` made of thedipicrylaminatesof` sdium, lithium, or magnesium, but the calcium g saltis preferred. AAs to the quantity of dipicrylaminate .to ,be used, ithas been found advantageous to work without substantial excess or evenwith a slight deficiency of dipicrylaminate, calculated with iol.:z3-102) reference to the total potassium content of the solution, e. g.sea water, to be treated.

After separating the precipitated crystalline mass, the solution is madeacid by the addition water, salt lakes, mother liquors, etc. A charac- 5of an acid whereby any excess of precipitant (e. yteristic feature ofthe invention is the employg'. calcium dipicrylaminate) is decomposedand ment, `for this purpose, of dipicrylaminates, adinsolubledipicrylamine is precipitated, which vantage being taken of thesolubility `relationcanberecovered by ltration.

'ships ofthe latter. After filtration, the solution contains only It isknown that, for example, the potassium 1o traces of dipicrylamine.rubidium, and cesium salts of dipicrylamine 'I'he dipicrylamine may beprecipitated by '(hexanitrodiphenylamine)` are practically insolmeans ofany suitable acid, preferably a readily uble in water, while otherdipicrylamine salts available and inexpensive mineral acid, such as`(dipicrylaminates) such as those of sodium, lithhydrochloric acid orthe like.

ium, magnesium and calcium are readily soluble It has been foundadvantageous to carry out in water. l this precipitation in separatestages in order to The invention is based upon the recognition obtain`crystals suitable for filtration, and the that the aforementionedsolubility characterispreferred method of carrying` Out the said pretics'of the dipicrylaminates may be utilized, cipitation Will be describedbelow: without noteworthy `consumption of dipicryla- The lteredpotassium dpicrylamnte 1S de.- mine, for the recovery on a commercialscale of composed with the aidA of an acid which correpotas'sium saltsfrom salt solutions, such as sea sponds to the DOHSSUIII Salt t0 bePrepared, e. g. watenwherein the'content of potassium is very nitricacid, sulphuric acidor hydrochloric acid, gun-11,` whereby potassiumnitrate, potassium sulphate A, The possibility of the-technicalrealisation of 0I' DOtaSSllm ChlOrde iS fOImed, While free dithelprocessof the present invention is based, prylfimne Separates Gilt.,V v amongother things, upon the discovery that the In carrying out` the saiddecomposition b practically Water-insoluble potassium dipicrylmeans ofacid thas `been found that inv order aminate may bebrought to reactdirectly with .30 to obtain the most satisfactory results certain anacid, such, for example, as` nitricacid, suldegrees of concentration andcertain temperaphuric acid or hydrochloric acid, in such mantures mustbe used, said degrees cf concentraner that the potassium, combined withthe acid, tion and temperatures-being different in the lease goes intosolution, whileinsoluble'dipicrylamine of different acids. remains inithe form` of` substantially unaltered Thus when the decomposition iscarried Out by crysms y l i I means of nitric acid good results areobtained Wh-ilel the processof the present invention is When theconcentration of the acid does not exapplicable to a number of different`salt soluceed 20% and the temperature does not exceed {,ngwhich containpotassium, 'it is of particu- 30 C. In the interval of concentrationbetween lar advantage for the treatment of sea water due im 20% and 40%of nitric acid as well as in the temto'thefact that all the metals,`except potassium, perature interval between 30 C. and 80 C. the whichare present in the form of dissolved salts results are not satisfactorybut goed results are inthe sea water, form readily soluble compoundsagain obtained` with concentrations of 40-50% with dipicrylamina .4 andtemperatures above C'.

In order to recover potassium salts ,fromsalt "5 It is also possible tocarry out the decomposisolutions, in accordance with the invention, tionwith a nitric acid of a concentration above there is added to the saltsolution a solution of a 40% at low temperature in which case, however,readily soluble dipicrylamine salt, e. g. calcium the mixture should beheated afterwards in order dipicrylaminate, whereby the potassiumdipicryln to dissolve the potassium salt or otherwise the aminate isprecipitated `as a crystalline` mass 6o mixture may be dilutedsufficiently to cause solution of the potassium salt crystals.

If sulphuric or hydrochloric acid is used for the decomposition it hasbeen found necessary or at least preferable to` use comparatively highacid concentrations and comparatively high temperatures in order toavoid precipitation of the potassium salt formed.

It has further been found that the decomposition may easily take placeby means of organic acids such as acetic acid, in which case there isobtained a solution of potassium acetate.

Further the decomposition may also take place by means of carbon dioxide(CO2) under pressure in which case carbonate of potassium is produced.

After the decomposition has taken .placefsoy used for the furtherprecipitation oi potassium y dipicrylaminate from thepotassium-containing salt solution to be treated.

It has been established experimentally that it is possible in this wayto recover more than 70% of the potassium present in sea water.

The following illustrative example shows how the process may be carriedout for the production of potassium nitrate:

420 g. of dipicrylamine, HN(CsHz(NO2)3)2, dissolved in 8 liters of milkof lime with a content of 27 g. of CaO, were added, after preliminaryfiltration of the said solution, to 100 liters of sea water containingabout 73 g. of KCl, while stirring, at 1618 C. A red crystalline massseparated out, and this was filtered after minutes and then washed withwater. The filter cake weighed 435 g., of which '78% `was potassiumdipicrylaminate, KN(C6H2(NO2) 3) 2. The balance was water.

This lter cake was then treated while stirring at 20 C. with 270 cc. of14% nitric acid for about 3A hour, whereupon the crystalline mass`turned orange-yellow, having been converted by reaction with the. nitricacid without noteworthy alteration of the crystalline structure, intodipicrylamine, while the potassium vcontent of the crystals went intosolution as nitrate. Finally the mass was filtered and washed.

The quantity of potassiumnitrate in the solution (the filtrate)corresponded to a conversion of 93% of the used nitric acid. With asystemmatic treatment of the salt with nitric acid, practically completeconversion can be obtained.

To the first filtrate of 108 liters, containing unconverted calciumdipicrylaminate, there was added such a quantity of 47% nitric acid thata pH of 3.6 was obtained. Thiscaused precipitation of the`dipicrylaminate.

Results corresponding tothose given in the foregoing example were alsoobtained with other salt solutions containing potassium, e. g. with asalt solution of a composition corresponding to that of the water in theDead Sea.

As mentioned above, the precipitation" of dipicrylamine from thesolution, resulting after the recovery of the potassium salts, shouldpreferably be carried out in separate stages in order to obtain acomparatively coarse crystalline precipitation which lends itself easilyto filtration.

To the slightly alkaline solution obtained after the precipitation ofpotassium dipicrylaminate there is added, in accordance with thisfeature of the invention, a dilute acid in consecutive steps in suchA amanner lthat thesolution, for a certain period after each step,has apredetermined degree of acidity and` a predetermined concentration ofdipicrylamine dissolved.

Thereby it is possible to control the formation such a manner thatcomparatively large crystals are obtained. The degree of acidity at thelast step lies approximately at pH 3-4. It has been found thatpropitious conditions of precipitation are achieved when pH is changedapproximately one unit or less for each step, after precipitation hascommenced.

The dilution of the acid to be used for the precipitation is preferablycarried out by means of suspension or filtrate from a previous processof precipitation.

In the following an example will be given with reference to thediagrammatical drawing of how the lprocess may be carried out forobtaining 5,000 tons KzO per year from sea water using dipicrylamine asprecipitant and three stages in the process of recovering theprecipitation agent.

Eample 1750 cu. m. sea water, containing 0.43 kg. KzO per cu. m. arepumped per hour into a tankiA), to which therey are added per hour 50cu. m. of a solution of calcium dipicrylaminate, containing 5.6 tons ofdissolved dipicrylamine. Approximately of the KzO contents areprecipitated, corresponding to 0.57 ton K2O per hour. The precipitate isseparated on lter B and is removed for the production of potassium salt.To the filtrate, approximately 1800 cu. m., there are added 300 kg.nitric acid, diluted in approximately cu. m. return filtrate, or returnsuspension (C). Of this amount Vof dilute nitric acid there are used inthe rst stage (I) approximately 100 cu. m., whereby there is obtained apH of approximately 5.5. The liquid remains at this stage forapproximately ten minutes. y

The liquid is conveyed to the second stage (II) in which `furtherapproximately 20 cu. m. of the acid return liquid are added, wherebythere is obtained in this stage a pH of approximately Even in this stagethe liquid remains for approximately ten minutes. In the third stage(III) the rest of the acid return liquid, approximately 30 cu. m. isadded, wherebyy a pH of approximately 3.5 is arrived at. After tenminutes the liquid is conveyed to the filtering plant, in whichapproximately 300v kg.' dipicrylamine are recovered per hour.

The stepwise Aprecipitation here described results in a decidedimprovement of the velocity of filtration. 50 liters suspension,precipitated in three stages in accordance with the stepwise methodspeciiied, passed through a filtering surface of 1 dm.2 at a suction of500' mm. Hg in half an hour, whereas a` corresponding amount whenprecipitated in one stage needed two hours and ahalf. i

By the use of a pressure filter working at 8 kg. per sq. cm. a stillgreater improvementwas achieved, the filtering times being 31/2 minutesand 45 minutes respectively.

When it is mentioned above that nitric acid is added ini-order to makethe solution acid, it should be understood that any acid giving thenecessary degree of acidity may be used, provided it is suficientlycheap, itV being not feasible to recover this acid. Further, thetermstepwise precipitation is not to be taken in its strict sense, asV theprocess may well be carried out with a continuous current of liquorthrough the apparatuses, provided the time periodin Veach stage issufficiently long. vIt is even possible to 'use a precipitation tank or`channel with a continuous current of liquid, adding the acid at suitofvcrystals and the velocity of precipitation in able consecutive placesalong the current.

inate precipitated from sea Water is made to react with 100 cc. ofhydrochloric acid 36%, and after stirring for one hour at C. aconversion of 98% is obtained. A corresponding process with 79%sulphuric acid results in a conversion of 99% of the potassiumdipicrylaminate in 1/2 hour.

If higher temperatures and longer reaction periods are employedsatisfactory results may also be obtained in the case o hydrochloricacid with a concentration of approximately 10%.

We claim:

1. A process for the recovery of potassium salts from an aqueous salinesolution with a potassium content of the order of the potassium contentof sea Water and the like, comprising the steps of adding awater-soluble dipicrylamine salt to the solution to precipitate thepotassium in the form of Water-insoluble potassium dipicrylaminate,

` separating the precipitate of potassium dipicrylaminate from themother liquor, reacting the separated potassium dipicrylaminate with anacid to liberate dipicrylamine and to produce the potassium salt of thesaid acid in solution, and recovering non-converted dipicrylamine saltin the motor liquor in the form of free dipicrylamine by subjecting themother liquor containing said non-converted salt to the` action of anacid.

2. A process for recoveryof potassium salts from an aqueous salinesolution with a potassium content of the order of the potassium contentof sea water and the like, comprising the steps of adding awater-soluble dipicrylamine saltI to the solution to precipitate thepotassium in the form of Water-insoluble potassium dipicrylaminate,separating the precipitate of potassium dipicrylaminate from the motherliquor, reacting the separated potassium dipicrylaminate with an acid toliberate dipicrylamine and to produce the potassium salt of the saidacid in solution, and recovering non-converted dipicrylamine salt in themotor liquor in the form of free dipicrylamine by subjecting said motherliquor to the action in separate cons-ecutive steps of an acid.

3. A process for the recovery of potassium salts from an aqueous salinesolution with a -potassium content of the order of the potassium contentof sea water and the like, comprising the steps of adding awater-soluble dipicrylamine salt to the solution to precipitate thepotassium in the form of water-insoluble potassium dipicrylaminate,separating the precipitate of potassium dipicrylaminate from the motherliquor, reacting the separated potassium dipicrylaminate with an acid toliberate dipicrylamine and to produce the potassium salt of said acid insolution, and recovering non-converted dipicrylamine salt in the motherliquor in the form of free dipicrylamine by subjectingsaid mother liquorto the action in separate consecutive steps of a diluted acid.

4. A process for the recovery of potassium salts from an aqueous salinesolution with a potassium content of the order of the potassium contentof sea Water and the like, comprising the steps of adding awater-soluble dipicrylamine salt to the solution to precipitate thepotassium in the form of Water-insoluble potassium dipicrylaminate,separating the precipitate of potassium dipicrylaminate from the motherliquor, reacting the separated potassium dipicrylaminate with an acid toliberate dipicrylamine and to produce the potassium salt of the saidacid in solution, and recovering non-converted dipicrylamine salt in themotherliquor in the form of free dipicrylamine by subjecting said motherliquor to the action in separate consecutive steps of an acid dilutedwith solution from a previous process.

5. A process for 'the recovery of potassium salts from an aqueous salinesolution with a potassium content of the order of the potassium contentof sea Water and the like, comprising the steps of adding awater-soluble dipicrylamine salt to the solution to precipitate thepotassium in the form of` Water-insoluble potassium dipicrylaminate,separating the precipitate of potassium dipicrylaminate from the motherliquor, reacting the separated potassium dipicrylaminate with an acid toliberate dipicrylamine andto produce the potassium salt of the said acidin solution, and recovering non-converted dipicrylamine salt in themother liquor in the form of free dipicrylamine by subjecting saidmother liquor to the action in separate consecutive steps of an acid,the amount of acid added for each consecutive step being so determinedas to increase the degree of acidity between the consecutive stepsapproximately one unit of pH.

6. A process for the recovery of potassium salts from an aqueous salinesolution with a potassium content oi the order of the potassium contentof sea water and the like, comprising the steps of adding awater-soluble dipicrylamine salt to the solution to precipitate thepotassium in the form of Water-insoluble potassium dipicrylaminate,separating the precipitate of potassium dipicrylaminate from the motherliquor, reacting the separated potassium dipicrylaminate with an acid toliberate dipicrylamine and to produce the potassium salt offthe saidacid in solution, and recovering non-converted dipicrylamine salt in themother liquor in the form of free dipicrylamine by subjecting saidmother liquor to the action of diluted nitric acid in three consecutivestages, the amount of acid added at each stage being so determined as tocause an increase in the degree of acidity of approximately one unit pHfor each consecutive stage, the solution remaining in each stage for aperiod of approximately ten minutes.

'7. A method of treating aqueous saline solutions containing potassiumsalts which comprises the steps of isolating the potassium as potassiumdipicrylaminate and reacting the latter with nitric acid of aconcentration below 20% and at a temperature below 30 C. whereby thepotassium of the dipicrylaminate goes into solution as nitrate ofpotassium while dipicrylamine remains in crystalline form.

8. A method of treating aqueous saline solutions containing potassiumsalts, Which comprises the steps of isolating the potassium as potassiumdipicrylaminate and reacting the latter with nitric acid of aconcentration below 20% whereby the potassium of the dipicrylaminategoes into solution as nitrate of potassium while dipicrylaminate remainsin crystalline form.

JACOB KIELLAND. WILHELM FLEISCHER.

